Statement of the problem: Pressure ulcers are a common complication of immobility for elderly adults in health care facilities. Although clinical guidelines for pressure ulcer prevention recommend use of pressure-redistributing support surfaces (PRSS, i.e., mattresses and overlays designed to prevent pressure ulcers) and manual repositioning every two hours, there is little evidence that either of these interventions is effective. The degree of adherence to these recommendations is also unclear. Summary of methods: Secondary analysis of data from a 2004-2007 cohort study of patients age ≥ 65 years who underwent hip fracture surgery in nine hospitals in the Baltimore Hip Studies network (n=658). Study visits, which included full-body examinations and recording of support surfaces in use, were performed as soon as possible after hospital admission and on alternating days for 21 days. Information on repositioning frequency was collected from patient charts for the first five days of hospitalization. Results: The rate of incident pressure ulcers stage 2 or higher per person-day of follow-up did not differ significantly between patients using pressure-redistributing mattresses (relative rate 0.9, 95% CI 0.6-1.3) or those using pressure-redistributing overlays (relative rate 0.7, 95% CI 0.4-1.2), compared to those not using PRSS. There was no significant association between pressure ulcer incidence rate and use of any of the nine types of PRSS, compared to not using PRSS. Similarly, among bedbound patients in the first five days of hospitalization, the rate of incident pressure ulcers stage 2 or higher per person-day of follow-up did not differ between patients repositioned at least every two hours and those repositioned less frequently (relative rate 1.1, 95% CI 0.5-2.4). During the first five days of hospitalization, bedbound patients were repositioned at least every two hours on only 53% of study visit days. Conclusions: This study did not provide evidence for decreased pressure ulcer incidence with the use of PRSS, or for decreased pressure ulcer incidence with use of frequent repositioning; these results do not support the allocation of substantial resources for these preventive measures. Additional study is needed to determine if these measures will prove effective in subpopulations at high risk for pressure ulcers.